Aviation training apparatus



C. BLENMAN, JR

AVIATION TRAINING APPARATUS Filed Feb. 18, 1943 3 Sheets-Sheet 1 INVENTOR Charles B LEnmaZ-IP. B'Y

Oct. 3, 1944.

Oct. 3, 1944. c. BLENMAN, JR

AVIATION TRAINING APPARATUS Filed Feb. 1a, 1945' 5 Sheets-Sheet 2 INVENTOR Eh ar'le 5 Eu'l enm art Jr. BY w fin-f0 NEY Oct. 3, 1944. c. BLENMAN, JR

AVIATION TRAINING APPARATUS Filed Feb. 18, 1943 s Sheets-Sheet s INVENTOR Eh. am]. E5 E1 ETLTTL an Jr.

Patented Oct. 3, 1944 UNITED STATES PATENT OFFICE (Granted under the m of March a, 1883, as amended April v30, 1928; 370 0. G. 757) r 13 Claims.

The present invention relates to aviation training apparatus and more particularly to apparatus of the stated character for training pilots to fly on radio range beams under conditions of actual flight where the usual radio range beacons are not available or are inconveniently situated.

Where pilots have completed their basic instrument training in flying on radio range beams producing aural signals, it is desirable to provide an'advanced formof controlled training under conditions of actual flight and to make provision upon completion of this advanced training for periodically reviewing this type of radio beam flying. While flight on regularly established radio range stations or beacons of the aural type-provides a satisfactory form of advanced training, such training is not always pos-. sible because of the volume of trafllc on the civil airways, the absence or relative inaccessibility of these radio range stations and the fact that the antenna systems-on some aircraft are not suited for satisfactory beam flying.

In order, therefore, to train pilots in radio beam flying under conditions of actual flight I where radio range stations or beacons of the aural type are not available, there is provided, in accordance with the present invention, an apparatus capable of producing an artificial aural radio range signal which is installed in the airplane used on the training flight. If such apparatus is to be effective for its intended purpose it is essential that it produce a realistic radio range signal, that it be under the control of an instructor or safety pilot and that it generate no radio frequency energy to avoid interference with the reception of the radio receiver carried by the airplane.

, The apparatus in the preferred embodiment of the present invention includes a conventional audio frequency oscillator coupled to two amplifiers through any suitable radio range keying unit. This unit keys theoscillator to produce the two signals conventionally employed to designate pairs of radio range quadrants and impresses the signals so produced upon their respective amplifiers. Provision is made for varying the volume and relative intensities of the signals so that the instructor may produce any desired radio range signal. The output sides of the amplifiers are connected to pass the generated signal through the audio stage of the usual radio receiver carried by the airplane, thus producing'a realistic aural signal in which the signal simulating the desired signal of the radio range beacon is projected against the usual background noises of the receiver.

With the apparatus of the present invention it is possible for the instructor or safety pilot to exactly reproduce the aural signal of a radio range station or beacon from an on-course signal, through all variations of a bisignal characteristic, to a single signal which is heard on the bisector of a radio range quadrant. Also by manipulating the volume control of the apparatus the instructor may simulate the conditions ob-,

taining on approaching and passing over a radio range beacon. In use the instructor operates the apparatus and orients the radio range signal with respect to lines of reference upon the surface of the earth, as will be pointed out more in detail hereinafter.

In the light of the foregoing it is an object of the present invention to provide an apparatus for training pilots under conditions of actual flight to fly on radio range beams producing aural signals where radio range stations or beacons of the aural type are not available.

It is another object of the present invention to provide an apparatus of the stated character wherein provision is made for varyingth'e volume and relative intensities of artificially generated audio frequency signals so that the instructor or safety pilot may produce any desired radio range signal corresponding to the instantaneous position of the airplane.

It is another and still further object of the present invention to provide an apparatus of the character noted above for producing a realistic artificial aural radio range signal in which the signal simulating the desired signal of the radio range beacon is projected against the usual background noises of the airplane receiver.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying sheets of drawings wherein:

Fig. 1 shows diagrammatically the electrical circuits of the radio range signal generator comprised of the oscillator, keying unit and amplitiers and the connections between th amplihers and the audio stage of the airplane receiver;

Figs. 2 and 3 are respectively plan and side elevational views of the keying unit forming a part of the signal generator;

Figs. 4A and 4B are partial sectional side elevational views taken on the line 4-4 of Fig,

3 showing the Morse code si nal cam and associated contactor of the keying unit in different phases of operation;

Fig. 5 is a partial sectional side elevational view taken on the line 8-8 of Fig. 3 showing certain details of the station identification signal cam and associated contactor of the keying unit;

Figs. 6A and 7A are partial sectional side elevational views taken on the lines 8-8 and 1-1 respectively of Fig. 3 showing the suppressor cams and associated contactors of the keying unit in a phase of their operation to suppress the signals of the Morse code signal cam but allow the signal of the station identification cam to be impressed upon one of the pair of amplifiers;

Figs. 63 and 7B are partial sectional side elevational views also taken on the lines 8-8 and 1-1 respectively of Fig. 3 showing the suppressor cams and associated contactors of the keying unit in another phase of their operation to suppress the signals of the Morse code signal cam but allow the signal of the station identification cam in be impressed upon the other of the pair of amplifiers; and

Fig. 8 is a partial side elevational view taken on the line 8-8 of Fig. 3 showing the suppressor cams and associated contacts of the keying unitcasing I in which are mounted the audio freqnency oscillator 2, the amplifiers 8 and 4 and the keying unit 8 for coupling the oscillator to the amplifiers. The casing I may be fabricated of any suitable material and is installedin the airplane to be accessible to the instructor or safety pilot and yet so as not to interfere with his control of the airplane. The component parts of the signal generator, it should be noted, are compactly assembled within the casing to produce a construction of limited over-all dimensions. This is highly advantageous since it not only makes the generator quite portable but facilitates installation of the same in the airplane.

The audio frequency oscillator 2 may be of any conventional prior art construction and is shown purely by way of illustration 'as of the tuned-grid circuit type employing a conventional triode 8 and an audio transformer I. The primary 8 of the transformer is connected to the plate 8 of the triode and the secondary iii to the grid H thereof, the secondary in together with the capacitor l2 and resistor I3 forming the tuned-grid or tank circuit. The circuit constants are to be A understood as having such values as to insure the generation of any desired audio frequency, a

frequency of 1,000 cycles having been found to 18 provides the necessary grid bias, while the 65 heater I8 for the cathode I1 is serially energized with those of the amplifiers 3 and 4 by any suitable source of electromotive force l8 acting through the dropping resistor i8 and switch 28. The plate supply voltage for the oscillator 2 is provided by any convenient source of electromotive force 2| connected with the primary 8 of the audio transformer through the conductor 22.

Any suiitable radio range keying unit 8 may be ing one type of keying unit that may be used in the apparatus of the -present invention there is shown in Figs. 2 and 3 a keying frame, identifled in general by the reference character 23, in-

s cluding the base plate 24 to which are secured the end bearing plates 28 and 28 and the intermediate bearing plate 21. The end bearing plate 28 is shown integral with the base plate 24, while the intermediate bearing plate 21 and the re- 10 maining end plate 28 are preferably removably the end bearing plates 28, 28 and the intermediate bearing plate 21 in any suitable manner, the bearing plates for this purpose being shown by way of illustration as provided with conically shaped recesses for receiving complementary shaped terminal portions of the cam shafts. A

Morse code signal or quadrant cam 32' and one or more station identification cams 33 are secured to the keying shaft 30, while a pair of suppressor cams 34 and 38 is shown secured to the remain- 25 ing cam shaft 3|. The cams may be fabricated of any suitable insulating material as Bakelite.

hard rubber or fiber and are splined or otherwise rigidly secured to their respective shafts.

A bracket consisting of the plate 38 is secured to the end plates 28 and 28 of the keying frame in any suitable manner, as by the bolts 31 and 38, and supports the contactors 38, 48, 4|, and 42 for cooperation with their respective cams 32, 33, 34 and 38. The Morse code cam contactor 35 38 and the suppressor cam contactors 4| and 42 are of identical construction and include respectively th movable code contact 43 for alternate engagement with the stationary contacts 44 and 48, the movable suppressor contact 48 for alternate engagement with the stationar contacts 41 5 but a single stationary contact 82 adapted to be engaged by a movable contact 83. The movable contact in each of the contactors is secured to a flexible electrically conductive blade 84 provided with terminal portions 88 and-88 bent or flexed 50 with respect to the intermediate contact supporting portion 81. 'I'heupper terminal portions 88 of the flexible blades 84 are arranged for engagement with the peripheral surfaces of their respective cams so that each cam may actuate its contactor at the proper time, while the lower flexed terminal portion 88 of each blade insures 1 that the movable contact will engage a stationary contact when the cams are not in positions to actuate the blades 84.

6o 3 As above noted the Morse code cam contactor 8 and the suppressor cam contactors 4| and 42 are identical in construction. For the details of construction reference is made to Figs. 4A, 6A and 7A wherein the stationary contacts are shown secured to electrically conductive blades 88 and 88. The blades 88 and 88 are spaced and electrically insulated from the flexible blade 84 by strips and 8| of any suitable insulating material, the strips and blades being perforated to 7 receive the terminally flanged metallic ferrules 82 for holding the blades 84. 88, 88 and strips 80, 8| in fixed superposed relation. An insulating sleeve 83 and insulating washers 84 are associated with the ferrules in the manner indicated employed for keying the oscillator. As illustrat- 18 to effectively insulate the three blades and their general by the reference character 8i.

ceived with equal intensities.

2,859,294 contacts from each other. The unitary contactors fashioned as described above are rigidly secured to the bracket 33 by the pairs of screws 53, as clearly shown in the drawings. The details of construction of the station identification cam contactor 40 are shown in Fig. 5. As there disclosed the electrically conductive blade 33 carrying the stationary contact is electrically insulated from the flexible blade 54 by the insulating strip 61, the blades and strip being held in fixed superposed relation by the metallic ferrules 38. insulating sleeves 69 and washers 10 all as in'the previously described contactors Screws 'll serve to secure the station identification cam contactor 40 to the bracket 35.

vThe motor frame 12 (Figs. 2 and 3) is rigidly securedto and spaced from the keying frame 33 by the bolts I3 and spacer sleeves I4 and includes the base plate 15 with which the bearing plate 16 is preferably integral. An electric motor 11 of any conventional prior art construction is secured to the base plate 15 in any suitable manner, as by the bracket I8 and screws 19, and has its shaft 80 connected to drive the keying shaft 30 through a suitable reduction gear identified in While the reduction gear may be of any convenient construction to obtain the desired rotative speed of the keying shaft, it is shown by way of illustration asconsisting of three pairs of spur gears 82, 83 and 84 supported in any suitable manner from the bearing plates 25 and IS. The suppressor cam shaft 3| in turn is driven by the keying shaft 30 through a still further'reduction gear 85 which may consist of two pairs of spur gears 86 and '81 suitably supported from the intermediate bearing plate 21. The gear ratio of the reduction gear 85 is chosen so as to establish the proper relation between the rotative speeds of the keying and suppressor shafts 30 and 3|. The motor 1'! (Figs. 1-3) is shown by way of example as of the direct current type and is connected for energization by the common source of electromotive force i8 upon closure of the switch 88.

While the Morse code signal or quadrantcam 32 may be cut to key any two letters of the Morse alphabet .for designating pairs of radio range quadrants, it is preferred to cut the cam in a manner to produce complementary interlocked code letters. This has the obvious advantage of producing a continuous and easily recognizable on-course signal when the code signals designating the different radio range quadrants are re- As illustrating a preferred configuration, the Morse code signal cam 32 (Figs. 4A and 4B) is shown cut to key the complementary code letters N and A which are conventionally employed for designating pairs of radio range quadrants. The stepped portions of the cam representing the letter N have recessed portions representing the letter A interspersed therewith to achieve interlocking of the code signals. In Fig. 4A the stepped portion of the signal cam 32 representing the dash of the,

letter N is in a position to actuate the flexible blade 54 of the contactor 39 and cause the movable contact 43 to engage the stationary contact 44. When the keying of the first part of the letter N has been completed the upper terminal portion 55 of the flexible blade 54 engages the recess of the signal cam representing the dot of the letter A causing the movable contact 43 to disengage the stationary contact 44 and engage the remaining stationary contact 45. After completing the keying of the first part of the letter a two amplifiers.

A the remaining parts of the letters N and A are successively keyed by the alternate engagement of the movable contact 43 with the stationary contacts 44 and 45. The positions occupied by the Morse code signal cam 32 and its contactor 38 shortly before completing a cycle of operation are shown in Fig. 4B. In this manner the code letters N and A may be keyed through any desired number of cycles to produce complementary interlocked signals.

While any desired number of station identification cams may be secured to the shaft 30 for keying the identification signal of the radio range station or beacon whose signal it is desired to simulate, the keying unit is shown for the sake of simplicity as provided with but the single station identification cam 33. This cam may be cut to key any arbitrary identification signal'and is shown for'illustrative purposes in Fig. 5 of the drawings as cut to key the code letters N and B of the Morse alphabet. The stepped portions of the cam 33 provide the proper spacing betification cam 33, on the other hand, causesthe movable contact 53 to engage the stationary contact 52 and results in the keying of the desired dots and dashes. Thus in a' single rotation of the cam 33 the contacts 52 and 53 are alternately engaged and disengaged to key the station identification signal consisting of the code letters N and B.

The suppressor cams 34 and 35 serve to alternately suppress the signals keyed. by the radio range quadrant cam 32 and the station identification cam 33. Thus in one phase of their operation the suppressor cams through the action of their associated contactors impress the signals keyed by the A and N quadrant cam on their respective amplifiers while suppressing the signal keyed by the station identification cam; and in a subsequent phase of their operation suppress the signals keyed by the A and N quadrant cam while alternately impressing the signals keyed by the station identification cam on the To the accomplishment of the foregoing the suppressor cam 34 and associated contactor 4| are arranged exclusively for cooperation with the amplifier-4 and the suppressor the movable and stationary contacts and-41 of the contactor 4| and the movable and stationary contacts 49 and 50 of the contactor 42 are engaged to permit transmission of the A and N signals while suppressing the station identification signal. As will be pointed out in detail hereinafter the engagement of the contacts 46 and 41 of the contactor 4| allows the A signal to be impressed exclusively on the amplifier 4 and the engagement of the contacts 49 and 50 of the contactor 42 allows the N signal to be impressed exclusively on the amplifier 3.

The subsequent suppression of the A and N signals and the alternate impression of the station identification signal on the two amplifiers is preferably achieved through cutting the suppressor cams 34 and 35 along a arc in an identical but complementary fashion as shown in Figs. 6A and 7A and by mechanically phasing these two cams on the suppressor cam shaft 3| as indicated in Fig. 8. The suppressor cams 34 and 35 are shown by way of illustration as cut to provide identical cam surfaces 83 in which a 33 arc of each surface permits engagement of themovable contact with the remaining stationary contact, when the 33 arc and terminal portion 55 of the flexible contactor blade are in juxtaposed relation. All other portions of the cam surface 83 hold the movable and both stationary contacts of the contactors out of engagement. By mechanically phasing the suppressor cams 34 and 35 to position the 30 cam surfaces as indicated in Fig. 8, alternate and successive impression of the station identification signal is assured.

Thus in the phase of operation of the suppressor cams depicted in Figs. 6A and 7A the movable contacts 43 and 43 of the contactors 4| and 42 have disengaged their respective stationary contacts 41 and 53 to suppress the A and N signals, the movable contact 43 of the contactor 42, however, having engaged the stationary contact 5| to impress the station identification signal on the amplifier 3. The arrangement is preferably such that a single revolution of the station identification cam 33 takes place while the terminal portion 55 of the fiexible blade of the contactor 42 and the 30? arc of the cam surface are in juxtaposed relation. Thus upon completion of a single revolution of the station identification cam 33 the identification signal will have been impressed on the amplifier 3 and the suppressor cams 34 and 35 will have been further rotated to cause the movable contact 43 of the contactor 42 to disengage its stationary contact 5| and to permit the movable contact 45 of the contactor 4| to engage its stationary contact 43, as clearly indicated in Figs. 6B and 7B. In the phase of operation of the suppressor cams illustrated in Figs. 6B and 7B the station identification signal is now being impressed upon the amplifier 4, the impression of the signal occurring during the second revolution of the station identification cam 33 and while the terminarportion 55 of the flexible blade of the contactor 4| and the 30 arc of the suppressor cam 34 are in juxtaposed relation.

In this manner alternate and successive impression of the station identification signal on the two amplifiers is insured while suppressing the A and N signals.

Since in the preferred construction described above one revolution of the station identification cam 33 with shaft 33 takes place during a 30 revolution of the suppressor cams 34 and 35 on the shaft 3|, it follows that the gear ratio of the intermediate reduction gear 85 must be 12:1 if the proper ratio between the rotative speeds of the keying and suppressor shafts 33 and 3| is to be established. In a cycle of operation of the keying unit, therefore, the keying shaft 33 will make nine revolutions and the suppressor shaft 3| three-quarters of a revolution during which the Morse code signal cam 32 and contactor 33 will key the letters A and N nine times, while the station identification signal being keyed by the station identification cam 33'and contactor 43 is being suppressed by the suppressor cams 34, 35 and contactors 4| and 42 as illustrated in Fig. 8. These nine revolutions of the keying shaft 33 are followed by three revolutions of this shaft and a one-quarter revolution of the suppressor shaft 3| and associated contactor 43 will key the station identification signal three times, while the A and N signals keyed by the Morse code signal cam 32 and contactor 33 are being suppressed by the suppressor cams 34, 35 and contactors 4| and 42 as illustrated in Figs. 6A and 7A and Figs. 6B and 'IB. Only two of the identification signals keyed by the station identification cam 33 and its contactor 43, however, are impressed on the amplifiers 3 and 4 by the action of the suppressor cams 34, 35 and their contactors 4| 42 for reasons already noted. The cycle of operation described above is then repeated, the period of each cycle being determined by the rotative speed of the keying shaft 33. In this connection a speed of from 15 to 20 revolutions of the key-v ing shaft per minute has been found to give a I convenient keying period.

In order to produce voltages corresponding to the keyed signals for subsequent impression on the amplifiers, a resistor 33 (Fig. 1) is arranged to be connected to the tuned circuit of the oscilcam contactor 43.

during which the station identification cam 33 lator 2 through the keying unit 5. The details of the electrical connections between the contactors of the keying unit 5, on the one hand, and resistor 33 and tuned circuit of the oscillator 2, on the other hand, for accomplishing this purpose are shown in Figs. 1, 4B, 5, 6A, and 7A. As

there indicated a common conductor 3| provided with a contact 32 slidably engaging the resistor I3 of the tuned circuit is connected to the conductors 33 and 94 secured respectively to the fiexible blades 54 of the Morse code and station identification cam contactors 33 and 43. The flexible blades 54 of the suppressor cam contactors 4| and 42 in turn are connected by the respective conductors 35 and 33 to the terminals 31 and 33 of the resistor 33, which is provided with the sliding contact 93 having a ground in common with the resistor I3 of the tuned circuit. A conductor I33 interconnects the stationary contact 44 of the Morse code cam contactor 33 with the stationary contact 53 of the suppressor cam contactor 42, conductor I3| connects the other stationary contact 45 of the Morse code contactor 33 with the stationary contact 41 of the suppressor cam contactor 4|, and conductors I32 and I33 connect the remaining stationary contacts 45 and 5| of the suppressor cam contactors 4| and 42 with the stationary contact 52 of the station identification A switch I34 is optionally provided for interrupting the circuit of the station identification cam contactor 43 when this is desired. As will appear presently the slidable contact 32 cooperating with the resistor l3 of the tuned circuit provides a volume control for the keyed signals, while the slidable contact 33 cooperating with the resistor 33 makes it possible to vary the relative intensities of the keyed signals.

The circuit connections described above are such that the portions I35-and I33 of the resistor 33 between the terminals 31 and 33 and the grounded contact 33 are alternately connected in parallel with the portion I31 of the tank resistor I3 between the slidable contact 32 and ground, the letter N of the Morse code signal during this. connection being impressed solely on the resistor portion I35 and the letter A solely on the resistor portion I33. That this is so becomes evident from a consideration of the suppressor cams 34, 35 and their associated contactors 4|,v 42 in their phase of operation depicted in Fig. 8 where the movablecontacts 43 and 49 are engaged with their respective stationary contacts 41 and 50. When now the movable contact 43 of the Morse code contactor 39 (Figs. 1, 4A, and 4B) is moved by the cam 32 to engage the stationary contact 44 and commence keying the letter N, the slidable contact 92 of the tank resistor I3 is connected to the terminal 98 of the resistor 90. This connection is completed through the conductors 9| and 93, the contacts 43 and 44 of the Morse code contactor 39, the conductor I00, the contacts 49 and 50 of the suppressor cam contactor 42 and the conductor 96. By this connection the resistor portion I05 is placed in parallel with the portion I01 of the tank resistor and an audio frequency voltage is impressed on this combination of resistors corresponding to the dash of the code letter N.

Upon further rotation of the Morse code cam 32 with the contacts of the suppressor contactors still engaged as in Fig. 8, the flexible blade 54 of the Morse contactor 39 (Figs. 1 and 4A) moves to engage a recess of the Morse code cam 32 with the attendant engagement of the movable and stationary contacts -43 and 45 and keying of the dot of the letter A. In so doing the slidable contact 92 of the tank resistor I3 is disconnected from the terminal 98 of the resistor 90 and is connected instead to the terminal 91 thereof. This connection is completed through the conductors 9| and 93, the contacts 43 and 45 of the Morse code contactor 39, the conductor IN, the contacts 46 and 41 of the suppressor cam contactor 4| and the conductor 95. By this connection the other resistorportion I06 is placed in parallel with the portion I01 of the tank resistor and an audio frequency voltage is impressed on the combination of resistors corresponding to the dot of the code letter A. After completing the keying of the first part of the letter A, the remaining parts of the letters N and A are successively keyed by the alternate engagement of the movable Morse code contact 43 with the stationary contacts 44 and 45. In so doing the resistor portions 05 and I06 are alternately connected in parallel with the resistor portion I'I of the tank circuit, these connections being accompanied by the impression of audio frequency voltages on the pairs of connected resistors corresponding to the dot and dash of the code letters N and A respectively. It should thus be clear that with the contacts of the suppressor cam contactors engaged as shown in Fig. 8 complementary interlocked signal. voltages will be alternately impressed on the resistor portions I and I06, the letter N of the Morse code being impressed solely on the resistor portion I05 and resistor 90 on the assumption that the switch I04 is closed. This connection is completed through the conductors 9| and 94, the contacts 62 and 53 of the-station identification cam contactor 40,,the conductor I03, the contacts 49 and 3| of the suppressor cam contactor 42 and the conductor 96. By this connection the resistor portion I05 is placed in parallel with the portion I01 of the tank resistor and an audio frequency voltage is impressed on the combination of resistors corresponding to the dashes and dots keyed by the station identification cam.33 and its associated contactor 40.

Upon completion of a single revolution of the station identification cam 33 to key the signal as described above, the suppressor cams 34 and 35 (Figs. 1, 6B and 73) will have been further rotated to cause the movable contact 49 of the contactor 42 to disengage its stationary contact 5| and permit the movable contact 46 of the contactor 4| to engage its stationar contact 48. When now the station identification cam 33 allows the movable contact 53 to engage the sta tionary contact 52 to recommence keying the station identification signal, the slidable contact 92 of the tank resistor I3 will be connected to the remaining terminal 91 of th resistor 90. This connection is completed through the conductors 9| and 94, the contacts 52 and 53 of the station identification cam contactor 40, the ,conductors I03 and I02, the contacts 46 and 48 of the suppressor cam contactor 4| and the con- I ductor 95, By this connection the resistor por- 4| and 42 (Figs. 1, 6A and 7A) will move to disof its contactor 40 to engage the stationary contact 52 to begin keying the station identification "signal, the slidable contact 92 of the tank resistor I3 is again connected to the terminal 98 of the tion I06 is placed in parallel with the portion I01 of the tank resistor and an audio frequency voltage, as before, is impressed on the combination of resistors corresponding to the dashes and dots keyed by the station identification cam 33 and its associated contactor 40. It should thus be clear that with the contacts of the suppressor contactors positioned to suppress the A and N signals,'voltages corresponding to the identification signals will be alternately impressed upon the resistor portions I05 and I06.

The slidable contact 99 (Fig. 1) engaging the resistor makes it possible to vary the relative intensities of the signal voltages impressed upon the resistor portions 05 and I 06. Thus with the contact 99 positioned to engage the midpoint of the resistor 90 equal portions I05 and I06 of the resistor will be alternately connected in parallel with the resistor portion I0I of the tank circuit, with the result that the signal voltages impressed upon the resistor portions I05 and I06 will be equal. If, on the other hand, the slidable contact 99 is moved to a position on either side of its mid-position, it is evident that unequal resistor portions I05 and I06 will be alternately connected in parallel with the resistor portion I0'I of the tank circuit. In this position of the slidable contact '99, therefore, a, smaller signal voltage will 'be impressed across the smaller of the resistor portions I05 and I06 While a larger voltage will be impressed across the larger of the resistor portions. When the slidable contact 99 is finally moved into terminal engagement with the.resistor 90 all of this resistor will be connected in parallel with the resistor portion |0'| of the tank circuit in one phase of operation of the keying unit, while in a subsequent phase of its operation the resistor portion I01 of the tank circuit will be short-circuited. Under these circumstances maximum and zero signal voltages are alternately produced. By adjusting the slidable contact 92 along the tank resistor I3 the magnitude of the signal voltages across-the resistor portions I08 and I 06 may be controlled.

Thus it should be clear that the adjustable contact 99 in cooperation with the resistor 80 makes it possible to increase the amplitude of one signal voltage while simultaneously decreasing the amplitude of the other and that the ad- Justable contact 92 in cooperation with the tank resistor I2 controls the volume or magnitude of these signals. Both of the slidable contacts 92 and 99 are under the control of the instructor or safety pilot, who is thus able to produce signal voltages across the resistor portions I08 and I08 simulating those of a radio range beacon or station from an on-course signal, through all variations of a bisignal characteristic, to a single signal designating the bisector of a radio range quadrant. The signal voltage produced across the resistor portion I08 provides the excitation for the amplifier 2 and that produced across the resistor portion I06 the excitation for the amplifier 4. Since the letter N of the Morse code' signal is impressed solely on the resistor portion I08 and the letter A solely on the resistor portion I06, it follows that separate amplifiers are provided for amplifying the two signals conventionally employed for designating pairs of radio range quadrants.

The tubes of the amplifiers may be of any convenient prior art construction and are shown by wayof illustration as triodes I08 and I09 in which the respective heaters I I and III are connected with the heater I6 of the oscillator triod for series energization, all as previously noted. The cathodes H2 and II 2 are connected to the common cathode resistor II4 shunted by the usual by-pass condenser- I I8 to provide a source of grid bias for class A operation, while the grids H8 and I I1 are shown connected to the terminals 91 and 88 of the resistor 90. A variable impedance audio transformer IIO provides a proper match between the amplifiers, on the one hand, and the radio receiver and intercommunication system of the airplane, on the other hand. The adjustable contact II 9 associated with one end of the tapped primary I of this transformer is shown connected to the anodes I2I and I22 of the amplifiel's by the conductors I22 and I24, the remaining end of the primary 120 being connected to the common source of electromotive force 2I which serves as the plate supply voltage. The secondary I25 oi the audio transformer III is shown provided with a conventional jack I28 to receive the usual cable plug I21 so that the radio range signal generator described in detail above may be connected to the radio receiver carried by the airplane. From the foregoing it should be clear that the signal voltages produced across the resistor portions I08 and I06 provide the excitation for the amplifiers 2 and 4 respectively. For the input or control circuit of the amplifier 2 includes the cathode H2, the cathode resistor H4 shunted by the condenser N5, the resistor portion I05 and grid II8, while thatv of the amplifler 4 includes the cathode I I2, the cathode resistor II4 shunted by the condenser H8, the resistor portion I08 and the grid I I1.

The airplane radio receiver may be of any conventional prior art construction, only those portions of the receiver being shown in Fig. 1

' which are essential to an understanding of the present invention. As there indicated the receiver includes a casing I28 in which, among other things, there may be mounted one or more auation. The amplifier tube of the audio stage is shown by way of example as a tetrode I22 in which the control grid .I2I is to be understood as being connected to the detector stage through the conductor, I22, the coupling condenser I22, the

grid leak resistor I24 and the conductor I28.. The cathode I28 is connected to the cathode resistor I21 shunted by the usual by-pass condenser I28 to provide a source of grid bias, while the condenser I29 and dropping resistor I42 connected by the conductor I to the power supply provide the proper voltage for the screen grid I42: An audio transformer I42 has its primary I44 connected to the anode I48 and to the conductor I4I leading to the power supply and its secondary I48 connected in series with the load resistor I41. The conductor I48 connected with the grounded secondary terminal and the conductor I49 with its contact I80 slidably engaging the load resistor I41 provide the usual volume control for the receiver. Jacks I8I and I82 con-' nected to the input side of the audio stage I29 are arranged to receive the cable plugs I82 and I84 respectively so that the signal generator and the intercommunication system may be connected to the radio receiver. A jack I88 connected to the output side of the audio stage I29 through the conductors I48 and I49 is arranged to receive the cable plug I58 so that the control boxes for the pilot and instructor may also be connected with the receiver.

The radio range signal is impressed upon the audio stage of the receiver through the cable I81 interconnecting the signal. generator with the receiver and is heard as an audible signal in the headphones I88 and I89 of the respective control boxes I60 and I6I connected to the output side of the receiver audio stage by the cable I62. The headphones I58 and I89, it will be observed, are provided with plugs I82 and I64 for connection respectively with the jack I68 of the instructor's control box I60 and with the Jack I88 of the pilot's control box III. The jacks I65 and I86 in turn are connected to auxiliary volume controls consisting of the resistors I61 and I68 and slidable contacts I88 and I10, the two resistors I61 and I80 of the volume controls being connected in parallel across the terminals of the cable I82 by the conductors "I and I12 and the common ground. In order that the instructor and pilot may converse with each other while the airplane is in flight, an audio transformer I12 is provided with its secondary I14 connected by the inter-phone cable I18 to the input side of the receiver audio stage and with its primary I16 connected to the microphones I11 and I18 of the respective control boxes I60 and I6I. The microphones I11 and I18 are-also provided with plugs I12-and I80 for connection with the jacks I8I and I22 0! the respective control boxes I60 and I8I, these jacks in turn being connected to the primary I18 of the audio transformer through the common source of electromotive force I82.

There is thus provided an aviation training apparatus in which the output of the radio range signal generator is channeled through the audio stage of the airplane receiver to produce in the two headphones a realistic aural signal in which the signal simulating the desired signal. of the radio range beacon is projected against the usual background noises of the receiver. With this apparatus it is possible for the instructor or safety pilot through manipulation of the die amplifier stages I29 biased for class A operradio range signal control 99 (Fig. 1) of the generator to exactly reproduce the aural signal of a radio range station or beacon from an oncourse signal, through all variations of a bisignal characteristic, to a single signal-which is heard on the bisector of a radio range quadrant. Also by manipulating the volume control 92 (Fig.

l) of the signal generator, the instructor may simulate the conditions obtaining on approaching and passing over a radio range beacon. This latter feature is of considerable. importance. For the sure knowledge on the part of the pilot when passing through a cone of silence above the radio range station is indispensable to successful instrument flying. Finally,v it is to be observed that the instructor as well as the pilot hears the signal; grid that the instructor and pilot may converse with each other during the training flight as an aid in instructing the pilot. The fact that the instructor hears the signal is important, since by this arrangement it is possible for him to adjust the controls 92 and 99 (Fig. l) of the generator to produce a signal corresponding to the position of the airplane.

In use the instructor manipulates the controls of the signal generator and orients the signal with respect to lines of reference upon the surface of the earth which are assumed to represent beam legs or tracks. Any long straight line over the surface of the earth may be used 80 as a beam leg or track. Thus a long stretch of railroad right of way, a straight highway, a canal or the beach line or-section of a coast provide excellent beamtracks. Other roads or railroads which cross or intersect any on the 85 above may be used as other beam tracks and their intersection may serve to fix the position of the radio range station with its corresponding cone of silence. The actual reference lines or beam tracks to be used on an instrument 40 training flight are selected in advance by consulting a sectional airways .chart, an intersection therebetween fixing and being chosen as the radio range station. The magnetic bearings of the reference lines to be used are then plotted on sheets of paper of convenient size to provide reference charts for use by the pilot and instructor in assisting them to achieve a proper orientation during the, training flight. The A and N quadrants are marked on the reference charts following the standard designation of such sectors.

When the pilot is ready to commence his training the hood is closed over his cockpit and the. instructor, who is also the safety pilot, flies the airplane to a. location in one of the quadrants where he can fix the airplanes position visually with respect to the reference lines. The radio range signal generator in the instructors cockpit is then set in operation to produce a signal corresponding to the position of the airplane, and the controls are turned over to the pilot under the hood. From then on the instructor varies the signal and volume to correspond to the changes of position of the airplane. When-. as ever a reference line is intersected the pilot hears an on-course signal and when he flies directly over the intersection selected, the instructor manipulates the volume control of the signal generator to simulate passing through a cone of silence. Anyf'beam orientation problem including let-downprocedure can thus be simply and conveniently presented to a pilot undergoing training by an instructor who is familiar with the radio beam transmitter and who is 76 proficient at contact navigation and the judgment of distances on the ground from the air.

According to the provisions of the patent statutes I have set forth the principle and mode of any royalties thereon or therefor.

I claim: 1. An apparatus for simulating the aural signal of a radio range beacon adapted to an airplane radio for supplemental local communication comprising in combination an audio oscillator, means including a keying unit associated with the oscillator for producing complementary interlocked signals, amplifiers for the respective signals upon. which the signals are alternately impressed by the keying unit, means for simultaneously increasing the amplitude of one of the impressed signals while decreasing the amplitude of the other, and means associated with the output sides of said amplifiers for producing an aural signal simulating the desired signal of the radio beacon.

2. An apparatus for simulating the aural signal of a radio range beacon adapted to an airplane radio for supplemental local communication comprising in combination an audio oscillator, means including a keying unit associated with the oscillator for producing complementary interlocked signals, amplifiers for the respective signals upon which the signals are alternately impressed by the keying unit, means for simultaneously increasing the amplitude of one of the impressed signals while decreasing the amplitude of the other, a radio receiver, means for connecting the output sides of said amplifiers to the input side of the audio stage of said receiver, and means connected with the output side of said receiver for producing a realistic aural signal in which the signal simulating the desired signal of the radio range beacon is projected against the usual background noises of the receiver.

3. An apparatus for simulating the aural signal of a radio range beacon adapted to an airplane radio for supplemental local communication comprising in combination an' audio oscillator, means including a keying unit associated with the oscillator for producing complementary interlocked signals, amplifiers for the respective signals upon which the signals are alternately impressed by the keying unit, means for simultaneously increasing the amplitude of one of the" impressed signals while decreasing the amplitude of the other, a radio receiver, means for connecting the output sides of said amplifiers to the input side of the audio stage of said receiver and means connected with the output side of said receiver for producing a realistic aural signal for both the pilot and instructor in which the signal simulating the desired signal of the radio range beacon is projected against the usual background noises of the receiver.

4. An apparatus for instructing a pilot to fly on a radio beam the apparatus being adapted to an airplane radio for supplemental local communication comprising in combination a radio receiver and means under the control of the instructor for producing an audio frequency signal simulating the desired signal of a radio range beacon, the said signal producing means being connected to the radio receiver to produce a realistic aural signal in which the signal simulat- 'ing the desired signal of the radio beacon is projected against the usual background noises or the receiver.

5. An apparatus for instructing a pilot to fly on a radio beam the apparatus being adapted to an airplane radio for supplemental local communication comprising in combination a radio receiver, headphones for the pilot and instructor connected to the receiver and means including a pair of amplifiers with adjustable excitation under the control of the instructor for producing an audio frequency signal simulating the desired signal of a radio range beacon, the said signal producing means being connected to the radioreceiver to produce a realistic aural signal in the headphones in which the signal simulating the desired signal of the radio beacon is projected against the usual background noises of the receiver.

6. An apparatus for simulating the aural signal of a radio range beacon adapted to an airplane radio for. .supplemental local communication comprising in combination an audio oscillator,

means including a keying unit associated with the oscillator for producing artificial radio range signals, means for varying the ratio of the amplitudes of the signals, amplifiers for the respective signals upon which the signals are alternately impressed by the keying unit, and means associated with the output sides oi. said am'plifiers for producing an aural signal simulating the desired signal of theradio beacon.

sides of said amplifiers for producing an aural signal simulating the desired signal of the radio beacon.

8. An apparatus for. simulating the aural signal of a radio range beacon adapted to an airplane radio for supplemental local communi-' cation comprising in combination an audio oscillator, means including a keying unit associated with the oscillator for producing a series of complementary interlocked signals followed by beacon identification signals, means for varying the magnitude of the signals and the ratio of their amplitudes, amplifiers for the signals upon which the signals are alternately impressed by the keying unit, and means associated with the outout sides of said amplifiers for producing an aural signal simulating the desired signal of the radio beacon.

- 9. An apparatus for simulating the aural signal of a radio range beacon adapted to an airplane radio for supplemental local communication comprising in combination an audio oscillator, means including a resistor and a keying unit operable to connect portions of the same to the oscillator vfor producing'artificial radio range signals, a plurality of triode amplifiers between the grids of which the aforesaid resistor is connected and upon which the signals are alternately impressed by the keying unit, means for varying the ratio of the amplitudes of the signals and means associated with the output sides of said amplifiers for producing an aural signal simulating the desired signal oi! the radio beacon.

10. An apparatus for simulating the aural signal of a radio range beacon adapted to an airplane radio for supplemental local communication comprising in combination an audio oscillator, means including a resistor and a keying unit operable .to connect portions of the same to the oscillator for producing complementary interlocked signals, a plurality of triode amplifiers between the grids of which the aforesaid resistor is connected and upon which the signals are alternately impressed by the keying unit, means for varying the magnitude of the signals and the ratio of their amplitudes, and means associated with the output sides of said amplifiers for producing an aural signal simulating the desired signal of the radio beacon.

' 11. An apparatus for simulating the aural signal of a radio range beacon adapted to an airplane radio for supplemental local communication comprising in combination an audio oscillator, a plurality of amplifiers in the control circuit of each of which there is included a resistor, a keying unit for alternately connecting the resistors to the oscillator to produce voltages thereacross corresponding to the radio range signals, and means associated with the output sides of said amplifiers for producing an aural signal simulating the desired signal of the radio beacon. V

12. An apparatus for simulating the aural signal of a radio range beacon adapted to an airplane radio for supplemental local communication comprising in combination an audio oscillator, a plurality of amplifiers in the control circuit of each of which there is included a variable resistor, means for reciprocally varying the magnitudes of the resistors, a keying unit for alternately connecting the resistors to the oscillator to produce voltages thereacross corresponding to the radio range signals, and means associated with the output sides of said amplifiers for producing an aural signal simulating the desired signal of the radio beacon.

13. An apparatus for simulating the aural signal of a radio range beacon adapted to an airplane radio for supplemental local communication comprising in combination an audio oscillator the tuned circuit of which includes a load resistor, a plurality of amplifiers in the control circuit of each of which there is included a variable'resistor, means for reciprocally varying the magnitudes of the amplifier resistors, a keying unit for alternately connecting the amplifier resistors in parallel with a selected portion of the oscillator resistor to produce voltages across the amplifier resistors corresponding to the radio range signals, and means associated with the output sides of said amplifiers for producing an aural signal simulating the desired signal of the radio beacon.

CHARLES BLENMAN, JR. 

